1. Field of the Invention
The present invention relates to a diffraction grating device, a laser diode, and a wavelength tunable filter.
2. Description of the Related Art
Non-Patent Document 1 (Optical integrated device, Kohroh Kobayashi, Kyoritsu Shuppan Co., Ltd., 1999, p. 116) describes a wavelength tunable laser including a pair of non-uniform gratings. The non-uniform gratings have a plurality of peaks of reflectivity in a reflection spectrum thereof. In addition, a gain region (active layer) is provided between the pair of non-uniform gratings. In this wavelength tunable laser, the lasing wavelength is changed by injecting a current to each of the non-uniform gratings. Furthermore, by using the vernier effect, the lasing wavelength is significantly changed by injecting a small current into each of the non-uniform gratings. A sampled grating and a super-structure grating are described as the structure of the non-uniform grating.